The invention relates to an apparatus and a method for detection and segregation of faulty cigarettes in a production/packaging installation for cigarettes having an apparatus by means of which faulty cigarettes are segregated from the conveyed sequence of cigarettes.
In cigarette production, care is generally taken to ensure that there is an increased tobacco density at the burning end of the cigarette, in order to prevent tobacco from falling out as a result of the quite varied movements of the cigarette when being transported between the cigarette machine and the packing machine, or else subsequently within the packaging. Nevertheless, tobacco falls out of the end of the cigarette repeatedly when, for example, the tobacco becomes too dry. The presence of loose tobacco or of cavities at the cigarette ends leads to a poorer quality product. Efforts have therefore been made for many years in the process of cigarette manufacture in order to prevent the occurrence of such faulty cigarettes, in particular by means of experiments to detect such defects and to reject faulty cartons or cigarettes.
Until now, electromechanical methods with a stamp or a large number of stamps, or optical or infrared measurement methods, have primarily been used as the methods for detection of faulty cigarette ends.
In the case of electromechanical methods, which have been known for decades (see for example GD application U.S. Pat. No. 4,376,484 A dated Mar. 15, 1983 or DE 3 439 945 dated Jun. 20, 1985), a stamp or a group of stamps is moved towards the cigarette ends, and the penetration depth is recorded. For an optimum measurement result, the cigarette must for this purpose be stopped exactly at the position of the stamp, and any slight overlap of the stamp with the paper area of the cigarette would corrupt the measurement result. At the speeds which occur nowadays in the packing machine, this would mean a measurement device that is highly sensitive to mechanical destruction in the machine, with a negative influence on the possible transport and machine speeds. Particularly in the input area, where rapid and precise positioning for individual detection and individual ejection is extremely difficult, this measurement method has been found to be too inaccurate. Furthermore, the product is adversely affected by the mechanical contact with the stamp. This method can only inaccurately detect certain critical shapes of a point in which there is no tobacco, but which occur frequently, such as that of a cone in which there is no tobacco at the edge of the cigarette but tobacco is still present in the center.
In order to overcome these shortcomings, non-contacting methods have been developed repeatedly in the last 30 years, which are based on the back-scattering of light in the visible band or in the infrared band (see, for example, BAT, DE 2 236 218 A dated Mar. 29, 1973 or AMF Inc., DE 2 625 001 A dated Dec. 16, 1976 or Burrus S A, U.S. Pat. No. 4,742,668 A dated May 10, 1988). These methods have the advantage that the cigarettes need not be stopped as their end surfaces move transversely through the measurement zone of the sensors. This allows higher production rates. On the other hand, the measurement effect that is used here of reflection of the light on the cross-sectional surface of the cigarette is a pure surface effect. In consequence, even a single tobacco fiber which conceals a tobacco hole can make it impossible to detect this defect. In this case as well, conical defects which often occur in the center of the cross section but contain a small amount of tobacco at the paper edge cannot be identified. In addition, color fluctuations in the tobacco blend or fluctuations in the moisture in the tobacco result in a change in the reflection behavior, so that there is a relatively high level of measurement uncertainty in the detection of defective cigarettes.
The object of the invention is to provide a method by means of which a noncontacting measurement can be carried out which records not only the surface but also areas located underneath it in the cigarettes.